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A solar system like the sun’s?

The search for a solar system resembling the sun’s has come up with a candidate. This week, a team of British, Australian and American researchers led by Hugh Jones of Liverpool John Moores University, in England, announced the discovery of a Jupiter-like planet in orbit around a star known as HD70642, about 90 light-years away from Earth.

These days, planets going round stars other than the sun are two a penny. What is significant about this one is that it moves in a nearly circular orbit some distance from a parent star that is similar to the sun, without any other big planets in closer orbits. That leaves room for small rocky planets to live between the big planet and its star, just as Mercury, Venus, Earth and Mars live between Jupiter and the sun.

Before any were actually discovered, planetary systems around other stars were expected to be broadly similar to the sun’s solar system. So it came as something of a surprise when the first were found to be completely different. In some, Jupiter-like gas giants (which are the only planets detectable at such distances) move in highly elliptical orbits, so that their distance from their parent stars varies enormously. In others, the gas giants are close to their stars, in contravention of what had been the accepted model of how solar systems are formed. Indeed, it had begun to look as though it was the sun’s system that was the odd one out.

This latest discovery does not prove that this conclusion is wrong—after all, about 100 solar systems are now known, and none but this new one is like the sun’s. It should, however, prevent theorists from rewriting the rules of planetary formation too hastily.

(adapted from The Economist)


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